High strength biological cement composition and using the same

Abstract

A hydraulic cement for biomedical applications. The cement sets in-situ, hardening when exposed to water to produce nano-dispersed composite of calcium-silicate-hydrate gel mixed with hydroxyapatite. In comparison with prior cements, the composition provides high biocompatibility, high bioactivity and high biomechanical strength, due to the composite structure of the calcium silicate hydrate reinforced with co-precipitated particles of hydroxyapatite. Biocompatibility is also increased due to an absence of aluminum and magnesium in the composition. The cement is suitable for variety of applications, including dental implants, bone fixation, and bone repair.

Description

RELATED CASES [0001] This application claims the priority of Provisional Patent Application Ser. No. 60 / 731,561, filed Oct. 31, 2005.BACKGROUND OF THE INVENTION [0002] a. Field of the Invention [0003] The present invention relates generally to hydraulic cements for medical and dental applications, and, more particularly, to an aluminum-and magnesium-free hydraulic cement that produces a nano-dispersed composite of calcium-silicate-hydrate gel mixed with hydroxyapatite, that exhibits good mechanical strength and high biocompatibility and bioactivity. [0004] b. Related Art [0005] Hydraulic cements are commonly utilized in construction and also in medical and dental applications. [0006] One of the most important hydraulic cements is calcium di-silicate and tri-silicate-based cement, which is widely used in construction. There are three main compounds in the cement: dicalcium silicate (C2S), tricalcium silicate (C3S), and calcium aluminate (C3A). Highly crystalline calcium hydroxide (Ca...

AI Technical Summary

Benefits of technology

[0026] The present invention provides a new composition of hydraulic cement, and methods for making and using the composition for biomedical and dental applications. The new hydraulic cement has high mechanical strength, high bioactivity, and high biocompatibility. The cement is resistant to corrosion and is stable and durable in variety of environments, including biological environments. The cement sets at room or near-room temperatures and does not resorb (dissolve) in a biological environment.

[0027] The cement of the present invention is an aluminum-free and magnesium-free phospho-silicate hydraulic cement. The cement comprises oxides of calcium, phosphorous and silicon, and excludes magnesium and aluminum in any form. Although free of magnesium and aluminum compounds, the new cement rapidly gains strength through hydration-assisted setting at room temperature and pressure. As a result, it has high early strengths, high overall compressive strength, adjustable setting times, low hydration heat, and resistance to chemical degradation.

[0031] As a result, the biocement of the present invention has enhanced functionality, in particular enhanced strength and corrosion and dissolution resistance due to the absence of CH, combined with enhanced biocompatibility and bioactivity due to the presence of HAP and / or other phosphate inclusions. The HAP inclusions produced reactively in-situ also contribute substantially to the overall compressive strength of the set cement, both directly (through bonding to the C—S—H structure) and indirectly (through removal of the structurally weak CH inclusions). Additionally, HAP is much more resistant to environmental effects than CH, rendering the CPSC of the present invention more resistant to corrosion.

[0032] Silicate nanoparticles may optionally be introduced into the cement composition of the present invention to improve mechanical, setting, and biological properties. The silicate nanoparticles may suitably be in a colloidal silica solution that is mixed with the biocement powder. Silicate nanoparticles can be mixed with the biocement powder by ball milling. The colloidal nanoparticle will speed up the hydration of calcium silicate compounds and increase mechanical strength. Also, the silicate can enhance biocompatibility and bioactivity of biocement.

[0033] Furthermore, for dental applications, radio-opaque materials may be added to the composition to enhance absorption of X-rays, for improved visibility of the cement under X-ray examination. Examples of radio-opaque materials suitable for dental applications include, but are not limited to, barium sulfate, zirconium oxide, bismuth oxide, tantalum oxide, and mixtures thereof. Radio-opacity is very desirable in the cases of dental fillings and sealings; for some applications, however, it is not necessary to have high radio-opacity, for instance, pulp capping or in many orthopedic applications.

Problems solved by technology

The calcium hydroxide component, which is formed as a result of the setting reaction, negatively effects the quality of the set cement, since CH is soluble in water and has low strength.

However, the MTA composition derived from Portland cement is gray in color, which is unsuitable for many dental applications.

Moreover, among other problems, MTA contains significant amounts of aluminum and consequently presents certain biocompatibility and toxicity concerns, as will be discussed below.

However, this process only decreases the iron content and does not improve the biological properties of the material, since it still contains aluminum.

The material is designated for treatment of hazardous wastes, such as nuclear waste, to prevent leaching, and also for construction materials and structural materials, which would include relatively high levels of impurities and consequently exhibit toxicity unsuitable for medical / dental use.

The presence of aluminum is a major disadvantage of the materials derived from Portland cement (such as MTA or WMTA) when used for biomedical and dental applications.

Research indicates that aluminum ions are toxic to the human biological system.

For example, aluminum inhibits mineralization of bone, and is toxic to osteoblasts.

Aluminum also has adverse effect on red blood cells, parathyroid glands and chromosomes.

If the aluminum were to be removed from such compositions, the strength increase would be much slower, rendering the cement useless for its intended applications.

A number of disadvantages limit the applications of the process, such as the need for hydrothermal treatment for formation of the hydroxyapatite, and the need for high pressure (28 MPa) pressing in order to achieve an adequately high strength.

Also, the process described by Ma et al can not be used for forming a uniform composite structure, and the mechanical strength was not significantly improved by comparison with Ordinary Portland cement (OPC).

Hydroxyapatite (HAP) powder may be introduced into the composition by admixing an HAP powder into the other powder; there is no provision for reactive, in-situ formation of HAP, which limits the possibilities of composite formation, and also provides less than satisfactory mechanical properties and bioactivity / biocompatibility in the set material.

However, the mechanical properties were not improved when the samples were hydrated at room temperature.

The major drawback of CPC technology is low mechanical strength (generally below 20 MPa compressive), which severely limits its suitability for medical / dental materials and devices.

However, substantial elimination of flaws in CPC setting in contact with living tissue such as bone or dentine may be impractical or impossible.

In some situations it is also not desirable, as hard tissue such as bone may integrate easier with porous CPC as compared to dense CPC.

Unfortunately, although chemically advantageous, bio-glass must be processed at very high temperatures (generally in excess of 1000 C), and is a rather dense, weak and brittle material.

Another disadvantage of bio-glass is that it does not easily dissolve in biological environments (due to dense SiO2 film coverage), which is desirable in some applications, e.g. for stimulation of bone growth.

Unfortunately the need for the high temperature treatment makes this composite material difficult to apply as biomaterial, as all the processing and shaping operations must take place outside of the application site.

The need for high-temperature processing of the biomaterials is a drawback of this approach as well, similar to the bioglass described above.

However, in many applications, such as endodontics or orthopedic applications where the cement must have sufficient strength at all times, resorption is not desirable.

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